1. Field of the Invention
The present invention relates to an optoelectronic device, and relates more particularly to a flip-chip semiconductor optoelectronic device and a method for fabricating the same.
2. Description of the Related Art
Light emitting diodes are electronic devices that can convert electricity into light and have diode characteristics. Particularly, light emitting diodes only emit light when voltage is applied to their electrodes, and can emit stable light when direct current is supplied. However, light emitting diodes blink when alternating current is supplied, and the blinking frequency is determined by the frequency of the alternating current. The lighting theory of light emitting diodes is that electrons and holes in semiconductor material combine to produce light under an externally applied voltage.
Light emitting diodes have significant advantages of long lifespan, low heat generation, low electricity consumption, energy conservation, and pollution reduction. Light emitting diodes are widely adopted; however, their low light emitting efficiency is one problem that still needs to be resolved.
Packaged light-emitting diode devices can be categorized into horizontal type light-emitting diode devices and vertical type light-emitting diode devices. FIG. 1A shows a conventional wire-bonded semiconductor device, and FIG. 1B shows a flip-chip bonded semiconductor device. The horizontal type light-emitting diode device uses non-conductive substrate such as a sapphire substrate for an epitaxial process, and has an n-type electrode 105 and p-type electrode 107 both disposed on the same side of the device. Device packaging techniques include a wire-bonding technique and a flip-chip bonding technique. As shown FIG. 1A, a semiconductor optoelectronic chip 123, packaged using the wire-bonding technique, is directly bonded to a packaging substrate 115 and wires 311 are then used to electrically connect the semiconductor optoelectronic chip 123 to the packaging substrate 115. As shown in FIG. 1B, the flip-chip bonding method initially flips the semiconductor optoelectronic chip 123 over and mounts the semiconductor optoelectronic chip 123 on the packaging substrate 115 with bumps 113 for fastening and electrically connecting both. The wire-bonding technique is presently most widely adopted, suitable for rapid and mass production. By contrast, no electrodes and wires are disposed on the active surface of a flip-chip light-emitting diode chip, avoiding the problem of partial light-blocking that occurs with the wire-bonding technique. Therefore, a flip-chip light-emitting diode chip can emit more light compared to a wire-bonded light-emitting diode chip. In addition, a flip-chip light-emitting diode chip is raised higher by bumps, and has better heat dissipation compared to a wire-bonded light-emitting diode directly bonded to a packaging substrate.
The vertical type light-emitting diode device is a recently developed light-emitting diode device, which uses an electrically conductive substrate such as a silicon carbide in replace of a sapphire substrate, or is manufactured using a lift-off technique separating a sapphire substrate from a light-emitting diode. Moreover, the first electrode 215 of a vertical type light-emitting diode device can be either an n-type electrode or a p-type electrode, and the first electrode 215 and the second electrode 217 are disposed opposite to each other, wherein when the first electrode 215 is an n-type electrode, the second electrode 217 is a p-type electrode; when the first electrode 215 is a p-type electrode, the second electrode 217 is an n-type electrode. Referring to FIG. 2, during a packaging process, the first electrode 215 is directly bonded to the packaging substrate 115, and the second electrode 217 is wire bonded to electrically connect to the packaging substrate 115 using wires 311. The vertical type light-emitting diode devices can have better heat dissipation and emit more light compared to the horizontal type light-emitting diode devices. In particular, after the substrate for the epitaxial process is removed using a lift-off process, the electrical conductivity of the light-emitting diode devices is improved. However, the second electrode 217 is formed on the light-emitting region, and when the light-emitting diode device emits light, the second electrode 217 blocks a portion of emitted light, affecting the luminous intensity of the light-emitting diode device. Specially, if the light-emitting region is small, the blocked area on the light-emitting region is comparatively large, and the luminous intensity is more significantly affected. In theory, if the problem of electrodes blocking emitting light can be avoided, light-emitting diodes packaged using a flip-chip technique can have improved heat dissipation and higher luminous intensity. However, such a problem is difficult to avoid because the manufacturing processes of light-emitting diode devices cannot be easily changed. FIGS. 3A to 3C show a method of forming a flip chip light-emitting diode device. As shown in FIG. 3A, after a light-emitting structure 309 is formed on an epitaxial substrate 101, multiple first electrodes 215 are formed on the light-emitting structure 309. Next, the light-emitting structure 309 is then etched to show the n-type conductive layer. As shown in FIG. 3B, multiple second electrodes 217 are formed on the n-type conductive layer using a sputtering process. Multiple bumps 113 are separately disposed on the second electrodes 217 and the first electrodes 215 for electrical connection. Next, the epitaxial substrate 101 is removed. As shown in FIG. 3C, the individual light-emitting diodes are diced out. In fact, in the above-mentioned processes, several issues need to be resolved.
The first issue is in the etching process. The thickness ratio between the light-emitting structure 309 and the first electrode 215 may achieve a value of 1:20, and the light-emitting structure 309 can be exposed when the first electrode 215 thereon is completely removed. Therefore, the thickness of the first electrode 215 is a major factor that needs to be considered. However, the etching depth needed to expose the light-emitting structure is usually difficult to estimate. The second issue is related to the formation of the second electrode. Usually, the second electrode is formed using a sputtering process. As shown in FIG. 3A, the second electrodes 217 are formed within deep U-shaped spaces. Using a sputtering process to form second electrodes 217 within such deep U-shaped spaces 313 is difficult. In addition, the second electrode 127 is required to have a height equivalent to that of the first electrode 215, and each second electrode 127 must be suitably distant from the first electrode 215 and the light-emitting structure 209 such that short circuiting can be prevented and a sufficient space can be reserved for the dicing process. Forming an electrode within a deep U-shaped space 313 while following the aforementioned requirements make the manufacturing processes more difficult. The third issue is related to the thermal stresses between the first electrode 215 and the light-emitting structure 309. The electrode is mainly made of metal, and the light-emitting structure is made of Group III-V semiconductor compound. Generally, the thermal expansion coefficient of metal is higher than that of GaN material. Referring to FIG. 3B, when using a laser lift-off technique to remove the epitaxial substrate 101, the temperature may reach about 400 degrees C., and therefore, thermal stresses between the first electrodes 215 and the light-emitting structure 309 may develop, resulting in the deformation of the first electrodes 215 and damage to the light-emitting structure 309.
Thus, the present invention provides a flip chip semiconductor optoelectronic device without the above-mentioned issues.